Apparatus for processing plastic material

ABSTRACT

The invention relates to an apparatus for the pretreatment and subsequent conveying or plastification of plastics, with a container with a mixing and/or comminution implement that is rotatable around an axis of rotation, wherein, in a side wall, an aperture is formed, through which the plastics material can be removed, a multiscrew conveyor being provided, with at least two screws rotating in a housing, wherein the imaginary continuation of the longitudinal axis of the conveyor in a direction opposite to the direction of conveying passes the axis of rotation, where, on the outflow side, there is an offset distance between the longitudinal axis of the screw closest to the container, on the outflow side, and the radius that is parallel to the longitudinal axis, and in that the screws co-rotate.

The invention relates to an apparatus according to the preamble of claim1.

The prior art reveals numerous similar apparatuses of varying design,comprising a receiver or cutter compactor for the comminution, heating,softening and treatment of a plastics material to be recycled, and also,attached thereto, a conveyor or extruder for the melting of the materialthus prepared. The aim here is to obtain a final product of the highestpossible quality, mostly in the form of pellets.

By way of example, EP 123 771 or EP 303 929 describe apparatuses with areceiver (receiver container) and, attached thereto, an extruder, wherethe plastics material introduced into the receiver is comminuted throughrotation of the comminution and mixing implements and is fluidized, andis simultaneously heated by the energy introduced. A mixture withsufficiently good thermal homogeneity is thus formed. This mixture isdischarged after an appropriate residence time from the receiver intothe screw-based extruder, and is conveyed and, during this process,plastified or melted. The arrangement here has the screw-based extruderapproximately at the level of the comminution implements. The softenedplastics particles are thus actively forced or stuffed into the extruderby the mixing implements.

It is also known in principle that twin-screw extruders can be used andthat these can be linked to appropriate cutter compactors.

Many of these designs, which have been known for a long time, however,are unsatisfactory in respect of the quality of the treated plasticsmaterial obtained at the outgoing end of the screw, and/or in respect ofthe throughput of the screw. Especially when twin screws are used, thereare particular considerations which cannot be derived from the resultsfor single screws.

A distinction can be made between co-rotating and counter-rotating, andalso touching and tightly intermeshing, twin-screw conveyors ortwin-screw extruders, as a function of the axial distance thereinbetween the screws and of their relative direction of rotation.

In the case of co-rotating screws, the two screws rotate in the samedirection with identical angular velocities.

Each of these types has particular application sectors and uses. In thecase of the co-rotating twin-screw extruder, the conveying and thepressure increase are brought about in essence by virtue of the frictionbetween the stationary housing wall and the material rotatingconcomitantly with the screw, and the conveying effect is mainly aresult of drag flow. In the case of the counter-rotating twin-screwextruder, in contrast, the dominant principle is forced conveying.

Critical to the end quality of the product are, firstly, the quality ofthe pretreated or softened polymer material that enters the conveyor orextruder from the cutter compactor, and, additionally, the situation atintake and on conveying or, where appropriate, extrusion. Relevantfactors here include the length of the individual regions or zones ofthe screw, and also the screw parameters, such as, for example, screwthickness, flight depths, and so on.

In the case of the present cutter compactor/conveyor combinations,accordingly, there are particular circumstances, since the materialwhich enters the conveyor is not introduced directly, without treatmentand cold, but instead has already been pretreated in the cuttercompactor, viz. heated, softened and/or partly crystallized, etc. Thisis a co-determining factor for the intake and for the quality of thematerial.

The two systems—that is, the cutter compactor and the conveyor—exert aninfluence on one another, and the outcomes of the intake and of thefurther conveying, and compaction, where appropriate, are heavilydependent on the pretreatment and the consistency of the material.

One important region, accordingly, is the interface between the cuttercompactor and the conveyor, in other words the region where thehomogenized pretreated material is passed from the cutter compactor intothe conveyor or extruder. On the one hand, this is a purely mechanicalproblem area, requiring the coupling to one another of two differentlyoperating devices. Moreover, this interface is tricky for the polymermaterial as well, since at this point the material is usually, close tothe melting range, in a highly softened state, but is not allowed tomelt. If the temperature is too low, then there are falls in thethroughput and the quality; if the temperature is too high, and ifunwanted melting occurs at certain places, then the intake becomesblocked.

Furthermore, precise metering and feeding of the conveyor is difficult,since the system is a closed system and there is no direct access to theintake; instead, the feeding of the material takes place from the cuttercompactor, and therefore cannot be influenced directly, via agravimetric metering device, for example.

It is therefore critical to design this transition not only in amechanically considered way, in other words with an understanding of thepolymer properties, but at the same time to consider the economics ofthe overall operation—in other words, high throughput and appropriatequality. The preconditions to be observed here are in some casesmutually contradictory.

Co-rotating multi- or twin-screw conveyors must generally be operatedwith underfeed. With underfeed, the feed determines the throughput ofthe extruder, and material intake has to be very constant.

However, specifically in systems where there is a conveyor or extruderattached to a cutter compactor, the intake or feed into the twin-screwconveyor is anything but easy to adjust, and there is no possibility,for example, of metering by way of a gravimetric metering system. On thecontrary, in a cutter compactor the rotating mixing and comminutionimplements bring about continuous feed of the pretreated, softenedparticles or a continuous flow of material to the intake aperture of theconveyor or extruder.

In addition, another factor common to the known apparatuses is that thedirection of conveying or of rotation of the mixing and comminutionimplements, and therefore the direction in which the particles ofmaterial circulate in the receiver, and the direction of conveying ofthe conveyor, in particular an extruder, are in essence identical orhave the same sense. This arrangement, selected intentionally, was theresult of the desire to maximize stuffing of the material into thescrew, or to force-feed the screw. This concept of stuffing theparticles into the conveying screw or extruder screw in the direction ofconveying of the screw was also very obvious and was in line with thefamiliar thinking of the person skilled in the art, since it means thatthe particles do not have to reverse their direction of movement andthere is therefore no need to exert any additional force for the changeof direction. An objective here, and in further derivative developments,was always to maximize screw fill and to amplify this stuffing effect.By way of example, attempts have also been made to extend the intakeregion of the extruder in the manner of a cone or to curve thecomminution implements in the shape of a sickle, so that these can actlike a trowel in feeding the softened material into the screw.Displacement of the extruder, on the inflow side, from a radial positionto a tangential position in relation to the container further amplifiedthe stuffing effect, and increased the force with which the plasticsmaterial from the circulating implement was conveyed or forced into theextruder.

Apparatuses of this type are in principle capable of functioning, andthey operate satisfactorily, although with recurring problems:

By way of example, an effect repeatedly observed with materials with lowenergy content, e.g. PET fibres or PET foils, or with materials which ata low temperature become sticky or soft, e.g. polylactic acid (PLA) isthat when, intentionally, stuffing of the plastics material into theintake region of the extruder or conveyor, under pressure, is achievedby components moving in the same sense, this leads to premature meltingof the material immediately after, or else in, the intake region of theextruder or of the screw. This firstly reduces the conveying effect ofthe screw, and secondly there can also be some reverse flow of the saidmelt into the region of the cutter compactor or receiver, with theresult that flakes that have not yet melted adhere to the melt, and inturn the melt thus cools and to some extent solidifies, with resultantformation of a clump or conglomerate made of to some extent solidifiedmelt and of solid plastics particles. This causes blockage of the intakeand caking of the mixing and comminution implements. A furtherconsequence is reduction of the throughput or quantitative output of theconveyor or extruder, since adequate filling of the screw is no longerachieved. Another possibility here is that movement of the mixing andcomminution implements is prevented. In such cases, the system normallyhas to be shut down and thoroughly cleaned.

Problems also occur with polymer materials which have already beenheated in the cutter compactor up to the vicinity of their meltingrange. If overfilling of the intake region occurs here, the materialmelts and intake is impaired.

Problems are also encountered with fibrous materials that are mostlyorientated and linear, with a certain amount of longitudinal elongationand low thickness or stiffness, for example plastics foils cut intostrips. A main reason for this is that the elongate material is retainedat the outflow end of the intake aperture of the screw, where one end ofthe strip protrudes into the receiver and the other end protrudes intothe intake region. Since the mixing implements and the screw are movingin the same sense or exert the same conveying-direction component andpressure component on the material, both ends of the strip are subjectedto tension and pressure in the same direction, and release of the stripbecomes impossible. This in turn leads to accumulation of the materialin the said region, to a narrowing of the cross section of the intakeaperture, and to poorer intake performance and, as a furtherconsequence, to reduced throughput. The increased feed pressure in thisregion can moreover cause melting, and this in turn causes the problemsmentioned in the introduction.

Especially for co-rotating twin-screw conveyors, this type of stuffingeffect is counter-productive, and it is very difficult to avoidoverfeed.

It is therefore an object of the present invention to overcome thedisadvantages mentioned and to improve an apparatus of the typedescribed in the introduction in such a way as to allow the screws toachieve problem-free intake, even of materials that are sensitive orstrip-shaped, and to permit processing or treatment of these materialsto give material of high quality, with high throughput, while avoidingoverfeed of the conveyor.

The characterizing features of claim 1 achieve this object in anapparatus of the type mentioned in the introduction.

A first provision here is that the imaginary continuation of the centrallongitudinal axis of the conveyor, in particular extruder, if this hasonly a single screw, or the longitudinal axis of the screw closest tothe intake aperture, if the conveyor has more than one screw, in thedirection opposite to the direction of conveying of the conveyor,passes, and does not intersect, the axis of rotation, where, on theoutflow side, there is an offset distance between the longitudinal axisof the conveyor, if this has a single screw, or the longitudinal axis ofthe screw closest to the intake aperture, and the radius that isassociated with the container and that is parallel to the longitudinalaxis and that proceeds outwards from the axis of rotation of the mixingand/or comminution implement in the direction of conveying of theconveyor.

The direction of conveying of the mixing implements and the direction ofconveying of the conveyor are therefore no longer in the same sense, asis known from the prior art, but instead are at least to a small extentin the opposite sense, and the stuffing effect mentioned in theintroduction is thus reduced. The intentional reversal of the directionof rotation of the mixing and comminution implements in comparison withapparatuses known hitherto reduces the feed pressure on the intakeregion, and the risk of overfilling decreases. In this way, excessmaterial is not stuffed or trowelled with excess pressure into theintake region of the conveyor, but instead, in contrast, there is infact in turn a tendency to remove excess material from that region, insuch a way that although there is always sufficient material present inthe intake region, the additional pressure exerted is small or almostzero. This method can provide adequate filling of the screw and constantintake of sufficient material by the screw, without any overfilling ofthe screw with, as a further consequence, local pressure peaks where thematerial could melt.

Melting of the material in the region of the intake is thus prevented,and operating efficiency is therefore increased, maintenance intervalsare therefore lengthened, and downtime due to possible repairs andcleaning measures is reduced.

By virtue of the reduced feed pressure, displaceable elements which canbe used in a known manner to regulate the degree of filling of the screwreact markedly more sensitively, and the degree of filling of the screwcan be adjusted with even greater precision. This makes it easier tofind the ideal point at which to operate the system, in particular forrelatively heavy materials, for example regrind made of high-densitypolyethylene (HDPE) or PET.

Surprisingly and advantageously it has moreover been found thatoperation in the opposite sense, according to the invention, improvesintake of materials which have already been softened almost to the pointof melting. In particular when the material is already in a doughy orsoftened condition, the screw cuts the material from the doughy ringadjacent to the container wall. In the case of a direction of rotationin the direction of conveying of the screw, this ring would instead bepushed onward, and removal of an outer layer by the screw would not bepossible, with resultant impairment of intake. The reversal of thedirection of rotation, according to the invention, avoids this.

Furthermore, the retention or accumulation phenomena formed in the caseof the treatment of the materials which have been described above andare in strip form or fibrous can be resolved more easily, or do notoccur at all, since, at the aperture edge situated in the direction ofrotation of the mixing implements on the outflow side or downstream, thedirection vector for the mixing implements and the direction vector forthe conveyor point in almost opposite directions, or in directions thatat least to a small extent have opposite sense, and an elongate stripcannot therefore become curved around, and retained by, the said edge,but instead becomes entrained again by the mixing vortex in thereceiver.

The overall effect of the design according to the invention is thatintake performance is improved and throughput is markedly increased. Thestability and performance of the entire system made of cutter compactorand conveyor is thus increased.

In this connection, the applicant has found through experimentation, andrecognized, that precisely this non-aggressive intake resulting from thealtered direction of rotation of the implements has particularly goodsuitability for co-rotating twin-screw conveyors, since the lack ofstuffing effect assists underfeed, and overfeed effects are thereforeavoided. The intake is more controlled, and less pressurized, andthroughput is higher or operation is more reliable.

With this system it is possible to operate a co-rotating twin screw withunderfeed. Different modes of operation can be established for differentlevels of compaction. With heavy bulk densities, it is thus possible tomaintain a relatively low degree of compaction in the cutter compactor,and to create both underfeed and an adequate fill level. With lightstarting materials, the mode of operation with relatively highcompaction in the cutter compactor is selected, and the same effect canbe achieved.

Other advantageous embodiments of the invention are described via thefollowing features:

In particular, it is advantageous if there are precisely two screwsprovided or the conveyor is a co-rotating twin-screw conveyor. This cangive the most reliable results.

According to one preferred development of the invention, the screws arecylindrical and parallel to one another or the conveyor is a paralleltwin-screw conveyor, in particular in the form of twin-screw extruder.

According to an alternative development, the screws are conical or theconveyor is a conical twin-screw conveyor or conical twin-screwextruder. This type of conveyor has particularly good suitability forintake of low-weight flowable solids.

If one of the screws is longer than the other(s), preferably by a lengthgreater than or equal to three times the diameter of the screw, there isthe advantageous possibility of building up a melt pressure.

It is also possible that, at least in the region of the intake aperture,the screws intermesh tightly or touch, in order to comply with therequirements of the material to be treated.

According to another advantageous embodiment that saves space andprovides effective intake, one of the cross sections of the screws isvertically above the other, and the screws in the immediate region ofthe intake aperture are in particular symmetrical with respect to thecentre of the intake aperture and at an equal distance from the plane ofthe intake aperture.

In a possible alternative, one of the cross sections of the screws isobliquely above the other or horizontally alongside the other, and onlythe screw closest to the intake aperture is in the immediate region ofthe intake aperture.

In this connection, it is particularly advantageous for intakeperformance if the screws or the screw closest to the intake aperture,viewed from the starting point that is close to the intake or to thecontainer, where appropriate at the end close to the motor, of thescrews, or from the intake aperture, in the direction towards the end orthe discharge aperture of the conveyor, rotate(s) clockwise.

This is particularly advantageous for regrind materials, since these aregenerally very flowable. In known apparatuses with conventional screwrotation direction, material is charged to the screw solely through theeffect of gravity, and the implements have only little influence. Thismakes it difficult to introduce energy into the material, since it hasoften been necessary specifically to make a large reduction in theheight of the outer implements or even often to omit them. This in turnimpairs the melting performance in the screw, since the material has notbeen adequately heated in the cutter compactor. This is all the morecritical in the case of regrind materials, since regrind materials arethicker than foils, and it is all the more important that the interiorof the particles is also heated.

If the screw rotation direction is then reversed, material is no longerautomatically charged to the screw, and the implements are necessary forconveying the material into the upper region of the screw. This methodis also successful in introducing adequate energy into the material tofacilitate any subsequent melting. A further consequence of this isincreased throughput, and also better quality, since a higher averagetemperature of the particles can reduce shear in the screw, and this inturn contributes to improved MFI values.

The diameters of the screws are advantageously identical.

According to an advantageous development of the invention, the conveyoris arranged on the receiver in such a way that the scalar product of thedirection vector (direction vector that is associated with the directionof rotation) that is tangential to the circle described by the radiallyoutermost point of the mixing and/or comminution implement or to theplastics material transported past the aperture and that is normal to aradius of the receiver, and that points in the direction of rotation orof movement of the mixing and/or comminution implement and of thedirection vector that is associated with the direction of conveying ofthe conveyor at each individual point or in the entire region of theaperture or at each individual point or in the entire region immediatelyradially in front of the aperture is zero or negative. The regionimmediately radially in front of the aperture is defined as that regionwhich is in front of the aperture and at which the material is justabout to pass through the aperture but has not yet passed the aperture.The advantages mentioned in the introduction are thus achieved, andthere is effective avoidance of all types of agglomeration in the regionof the intake aperture, brought about by stuffing effects. In particularhere, there is also no dependency on the spatial arrangement of themixing implements and of the screw in relation to one another, and byway of example the orientation of the axis of rotation does not have tobe normal to the basal surface or to the longitudinal axis of theconveyor or of the screw. The direction vector that is associated withthe direction of rotation and the direction vector that is associatedwith the direction of conveying lie within a, preferably horizontal,plane, or in a plane orientated so as to be normal to the axis ofrotation.

In another advantageous formation, the angle included between thedirection vector that is associated with the direction of rotation ofthe mixing and/or comminution implement and the direction vector that isassociated with the direction of conveying of the conveyor is greaterthan or equal to 90° and smaller than or equal to 180°, where the angleis measured at the point of intersection of the two direction vectors atthe edge of the aperture situated upstream of the direction of rotationor of movement, in particular at the point that is on the said edge oron the aperture and is situated furthest upstream. This thereforedescribes the range of angles within which the conveyor must be arrangedon the receiver in order to achieve the advantageous effects. In theentire region of the aperture or at each individual point of theaperture, the forces acting on the material are therefore orientated atleast to a small extent in an opposite sense, or in the extreme case theorientation is perpendicular and pressure-neutral. At no point of theaperture is the scalar product of the direction vectors of the mixingimplements and of the screw positive, and no excessive stuffing effectoccurs even in a subregion of the aperture.

Another advantageous formation of the invention provides that the angleincluded between the direction vector that is associated with thedirection of rotation or of movement and the direction vector that isassociated with the direction of conveying is from 170° to 180°,measured at the point of intersection of the two direction vectors inthe middle of the aperture. This type of arrangement is relevant by wayof example when the conveyor is arranged tangentially on the cuttercompactor.

In order to ensure that no excessive stuffing effect occurs, thedistance, or the offset, between the longitudinal axis and the radiuscan advantageously be greater than or equal to half of the internaldiameter of the housing of the conveyor or of the screw.

It can moreover be advantageous for these purposes to set the distanceor offset between the longitudinal axis and the radius to be greaterthan or equal to 7%, or still more advantageously greater than or equalto 20%, of the radius of the receiver. In the case of conveyors with aprolonged intake region or with grooved bushing or with extended hopper,it can be advantageous for this distance or offset to be greater than orequal to the radius of the receiver. This is particularly true for caseswhere the conveyor is attached tangentially to the receiver or runstangentially to the cross section of the container.

In a particularly advantageous embodiment here, the longitudinal axis ofthe conveyor or of the screw or the longitudinal axis of the screwclosest to the intake aperture runs tangentially with respect to theinner side of the side wall of the container, or the inner wall of thehousing does so, or the envelope of the screw does so, where it ispreferable that there is a drive connected to the end of the screw, andthat the screw provides conveying, at its opposite end, to a dischargeaperture which is in particular an extruder head and which is arrangedat the end of the housing.

In the case of conveyors that are radially offset, but not arrangedtangentially, it is advantageous to provide that the imaginarycontinuation of the longitudinal axis of the conveyor in a directionopposite to the direction of conveying, at least in sections, passes, inthe form of a secant, through the space within the receiver.

It is advantageous to provide that there is immediate and directconnection between the aperture and the intake aperture, withoutsubstantial separation or a transfer section, e.g. a conveying screw.This permits effective and non-aggressive transfer of material.

The reversal of the direction of rotation of the mixing and comminutionimplements circulating in the container can certainly not result fromarbitrary action or negligence, and it is not possible—either in theknown apparatuses or in the apparatus according to the invention—simplyto allow the mixing implements to rotate in the opposite direction, inparticular because the arrangement of the mixing and comminutionimplements is in a certain way asymmetrical or direction-oriented, andtheir action is therefore only single-sided or unidirectional. If thistype of equipment were to be rotated intentionally in the wrongdirection, a good mixing vortex would not form, and there would be noadequate comminution or heating of the material. Each cutter compactortherefore has its unalterably prescribed direction of rotation of themixing and comminution implements.

In this connection, it is particularly advantageous to provide that themanner of formation, set-up, curvature and/or arrangement of the frontalregions or frontal edges that are associated with the mixing and/orcomminution implements, act on the plastics material and point in thedirection of rotation or of movement, differs when comparison is madewith the regions that, in the direction of rotation or of movement, areat the rear or behind.

In an advantageous embodiment here, on the mixing and/or comminutionimplement there are implements and/or blades which, in the direction ofrotation or of movement, have a heating, comminuting and/or cuttingeffect on the plastics material. The implements and/or blades can eitherhave been fastened directly on the shaft or preferably have beenarranged on a rotatable implement carrier or, respectively, a carrierdisc arranged in particular parallel to the basal surface, or have beenformed therein or moulded onto the same, optionally as a single piece.

In principle, the effects mentioned are relevant not only to compressingextruders or agglomerators but also to conveying screws that have no, orless, compressing effect. Here again, local overfeed is avoided.

In another particularly advantageous formation, it is provided that thereceiver is in essence cylindrical with a level basal surface and with,orientated vertically in relation thereto, a side wall which has theshape of the jacket of a cylinder. In another simple design, the axis ofrotation coincides with the central axis of the receiver. In anotheradvantageous formation, the axis of rotation or the central axis of thecontainer have been orientated vertically and/or normally in relation tothe basal surface. These particular geometries optimize intakeperformance, with an apparatus design that provides stability and simpleconstruction.

In this connection it is also advantageous to provide that the mixingand/or comminution implement or, if a plurality of mutually superposedmixing and/or comminution implements have been provided, the lowestmixing and/or comminution implement closest to the base is arranged at asmall distance from the basal surface, in particular in the region ofthe lowest quarter of the height of the receiver, and also that theaperture is similarly arranged. The distance here is defined andmeasured from the lowest edge of the aperture or of the intake apertureto the container base in the edge region of the container. There ismostly some rounding of the edge at the corner, and the distance istherefore measured from the lowest edge of the aperture along theimaginary continuations of the side wall downwards to the imaginaryoutward continuation of the container base. Distances with goodsuitability are from 10 to 400 mm.

It is moreover advantageous for the treatment process if the radiallyoutermost edges of the mixing and/or comminution implements almost reachthe side wall.

The container does not necessarily have to have a cylindrical shape withcircular cross section, even though this shape is advantageous forpractical reasons and reasons of manufacturing technology. Whencontainer shapes that deviate from the cylindrical shape with circularcross section, examples being containers having the shape of a truncatedcone or cylindrical containers which, in plan view, are elliptical oroval, a calculation is required for conversion to a cylindricalcontainer which has circular cross section and the same volume capacity,on the assumption that the height of this imaginary container is thesame as its diameter. Container heights here which are substantiallyhigher than the resultant mixing vortex (after taking into account thedistance required for safety) are ignored, since this excess containerheight is not utilized and it therefore has no further effect on theprocessing of the material.

The expression conveyor means mainly systems with screws that havenon-compressing or decompressing effect, i.e. screws which have purelyconveying effect, but also systems with screws that have compressingeffect, i.e. extruder screws with agglomerating or plastifying effect.

The expressions extruder and extruder screw in the present text meanextruders or screws used for complete or partial melting of thematerial, and also extruders used to agglomerate, but not melt, thesoftened material. Screws with agglomerating effect subject the materialto severe compression and shear only for a short time, but do notplastify the material. The outgoing end of the agglomerating screwtherefore delivers material which has not been completely melted butwhich instead is composed of particles incipiently melted only at theirsurface, which have been caked together as if by sintering. However, inboth cases the screw exerts pressure on the material and compacts it.

Further features and advantages of the invention are apparent from thedescription of the inventive examples below of the subject matter of theinvention, which are not to be interpreted as restricting, and which thedrawings depict diagrammatically and not to scale:

FIG. 1 shows a vertical section through an apparatus according to theinvention with extruder attached approximately tangentially with onescrew located above the other.

FIG. 2 shows a horizontal section through an alternative embodiment withextruder attached approximately tangentially with parallel cylindricalscrews located alongside one another.

FIG. 3 shows another embodiment with minimal offset of the extruder.

FIG. 4 shows another embodiment with relatively large offset of theextruder.

Neither the containers, nor the screws nor the mixing implements are toscale, either themselves or in relation to one another, in the drawings.By way of example, therefore, the containers are in reality mostlylarger, or the screws longer, than depicted here.

The cutter compactor/extruder combinations depicted in different viewsin FIG. 1 and FIG. 2 have very similar structure and are thereforedescribed together below. They differ mainly in the arrangement of thescrews 6 with respect to one another, a point on which more details willbe given below.

Each of the advantageous cutter compactor/extruder combinations depictedin FIG. 1 and FIG. 2 for the treatment or recycling of plastics materialhas a cylindrical container or cutter compactor or shredder 1 withcircular cross section, with a level, horizontal basal surface 2 andwith a vertical side wall 9 oriented normally thereto with the shape ofa cylinder jacket.

Arranged at a small distance from the basal surface 2, at most at about10 to 20%, or optionally less, of the height of the side wall 9—measuredfrom the basal surface 2 to the uppermost edge of the side wall 9—is animplement carrier 13 or a level carrier disc orientated parallel to thebasal surface 2, which carrier or disc can be rotated, in the direction12 of rotation or of movement indicated by an arrow 12, around a centralaxis 10 of rotation, which is simultaneously the central axis of thecontainer 1. A motor 21, located below the container 1, drives thecarrier disc 13. On the upper side of the carrier disc 13, blades orimplements, e.g. cutter blades, 14 have been arranged, and together withthe carrier disc 13 form the mixing and/or comminution implement 3.

As indicated in the diagram, the blades 14 are not arrangedsymmetrically on the carrier disc 13, but instead have a particularmanner of formation, set-up or arrangement on their frontal edges 22facing in the direction 12 of rotation or of movement, so that they canhave a specific mechanical effect on the plastics material. The radiallyoutermost edges of the mixing and comminution implements 3 reach a pointwhich is relatively close to, about 5% of the radius 11 of the container1 from, the inner surface of the side wall 9.

The container 1 has, near the top, a charging aperture through which theproduct to be processed, e.g. portions of plastics foils, is charged byway of example by means of a conveying device in the direction of thearrow. The container 1 can, as an alternative, be a closed container andcapable of evacuation at least as far as an industrial vacuum, thematerial being introduced by way of a system of valves. The said productis received by the circulating mixing and/or comminution implements 3and is raised to form a mixing vortex 30, where the product rises alongthe vertical side wall 9 and, approximately in the region of theeffective container height H, falls back again inward and downward intothe region of the centre of the container, under gravity. The effectiveheight H of the container 1 is approximately the same as its internaldiameter D. In the container 1, a mixing vortex 30 is thus formed, inwhich the material is circulated in a vortex both from top to bottom andalso in the direction 12 of rotation. By virtue of this particulararrangement of the mixing and comminution elements 3 or the blades 14,this type of apparatus can therefore be operated only with theprescribed direction 12 of rotation or movement, and the direction 12 ofrotation cannot be reversed readily or without additional changes.

The circulating mixing and comminution implements 3 comminute and mixthe plastics material introduced, and thereby heat and soften it by wayof the mechanical frictional energy introduced, but do not melt it.After a certain residence time in the container 1, the homogenized,softened, doughy but not molten material is, as described in detailbelow, removed from the container 1 through an aperture 8, passed intothe intake region of a twin-screw extruder 5, and received by screws 6there and subsequently melted.

At the level of the, in the present case single, comminution and mixingimplement 3, the said aperture 8 is formed in the side wall 9 of thecontainer 1, and the pretreated plastics material can be removed fromthe interior of the container 1 through this aperture. The material ispassed to a twin-screw extruder 5 arranged tangentially on the container1, where the housing 16 of the extruder 5 has, situated in its jacketwall, an intake aperture 80 for the material to be received by thescrews 6. This type of embodiment has the advantage that the screws 6can be driven from the lower ends in the drawing by a drive, depictedonly diagrammatically, in such a way that the upper ends of the screws 6in the drawing can be kept free from the drive. The discharge aperturefor the plastified or agglomerated plastics material conveyed by thescrews 6 can therefore be arranged at the said upper end, e.g. in theform of an extruder head not depicted. The plastics material cantherefore be conveyed without deflection by the screws 6 through thedischarge aperture; this is not readily possible in the embodimentsaccording to FIGS. 3 and 4.

There is connection for conveying of material or for transfer ofmaterial between the intake aperture 80 and the aperture 8, and in thepresent case this connection to the aperture 8 is direct and immediateand involves no prolonged intervening section and no separation. Allthat is provided is a very short transfer region.

In the housing 16, there are two cylindrical screws 6 with compressingeffect, each mounted rotatably around its longitudinal axis 15. As analternative, the screws can also be conical.

The extruder 5 conveys the material in the direction of the arrow 17.The extruder 5 is a conventional twin-screw extruder known per se inwhich the softened plastics material is compressed and thus melted, andthe melt is then discharged at the opposite end, at the extruder head.

In the case of the embodiment according to FIG. 1, one of the two screws6 is vertically above the other, and in the case of the embodimentaccording to FIG. 2 the two screws 6 are horizontally alongside oneanother.

The two screws 6 rotate in the same direction, and are thereforeco-rotating.

The mixing and/or comminution implements 3 or the blades 14 are atapproximately the same level as the central longitudinal axis 15 of thelowermost screw 6 in FIG. 1 or of the screw 6 adjacent to the intakeaperture 80. The outermost ends of the blades 14 have adequateseparation from the flights of the screws 6.

In the embodiments according to FIGS. 1 and 2, the extruder 5 is, asmentioned, attached tangentially to the container 1, or runstangentially in relation to its cross section. In the drawings, theimaginary continuation of the central longitudinal axis 15 of the lowerscrew 6 or of the screw 6 adjacent to the intake aperture 80 in adirection opposite to the direction 17 of conveying of the extruder 5towards the rear passes close to the axis 10 of rotation and does notintersect the same. On the outflow side, there is an offset distance 18between the longitudinal axis 15 of this screw 6 and the radius 11 thatis associated with the container 1 and that is parallel to thelongitudinal axis 15 and that proceeds outwards from the axis 10 ofrotation of the mixing and/or comminution implement 3 in the direction17 of conveying of the extruder 5. In the present case, the imaginarycontinuation of the longitudinal axis 15 towards the rear does not passthrough the space within the container 1, but instead passes it at ashort distance.

The distance 18 is somewhat greater than the radius of the container 1.There is therefore a slight outward offset of the extruder 5, or theintake region is somewhat deeper.

The expressions “opposite”, “counter-” and “in an opposite sense” heremean any orientation of the vectors with respect to one another which isnot acute-angled, as explained in detail below.

In other words, the scalar product of a direction vector 19 which isassociated with the direction 12 of rotation and the orientation ofwhich is tangential to the circle described by the outermost point ofthe mixing and/or comminution implement 3 or tangential to the plasticsmaterial passing the aperture 8, and which points in the direction 12 ofrotation or movement of the mixing and/or comminution implements 3, andof a direction vector 17 which is associated with the direction ofconveying of the extruder 5 and which proceeds in the direction ofconveying parallel to the central longitudinal axis 15 of the screw 6 iseverywhere zero or negative, at each individual point of the aperture 8or in the region radially immediately in front of the aperture 8, and isnowhere positive.

In the case of the intake aperture in FIGS. 1 and 2, the scalar productof the direction vector 19 for the direction 12 of rotation and of thedirection vector 17 for the direction of conveying is negative at everypoint of the aperture 8.

The angle α between the direction vector 17 for the direction ofconveying and the direction vector for the direction 19 of rotation,measured at the point 20 that is associated with the aperture 8 andsituated furthest upstream of the direction 12 of rotation, or at theedge associated with the aperture 8 and situated furthest upstream, isapproximately maximally about 170°.

As one continues to proceed downwards along the aperture 8 in FIG. 2,i.e. in the direction 12 of rotation, the oblique angle between the twodirection vectors continues to increase. In the centre of the aperture8, the angle between the direction vectors is about 180° and the scalarproduct is maximally negative, and further downwards from there theangle indeed becomes >180° and the scalar product in turn decreases, butstill remains negative. However, these angles are no longer termedangles α, since they are not measured at point 20.

An angle β, not included in the drawing in FIG. 2, measured in thecentre of the aperture 8, between the direction vector for the direction19 of rotation and the direction vector for the direction 17 ofconveying is about 178° to 180°.

The apparatus according to FIG. 2 represents the first limiting case orextreme value. This type of arrangement can provide a verynon-aggressive stuffing effect or a particularly advantageous feed, andthis type of apparatus is particularly advantageous for sensitivematerials which are treated in the vicinity of the melting range, or forproduct in the form of long strips.

FIGS. 3 and 4 serve merely to illustrate the connection possibilitiesfor the extruder with regard to the direction of rotation of theimplements. The drawings do not include the values for L, B and A.

FIG. 3 shows an alternative embodiment in which an extruder 5 with twoco-rotating screws 6, one located vertically above the other, isattached by its end 7, rather than tangentially, to the container 1. Thescrew 6 and the housing 16 of the extruder 5 have been adapted in theregion of the aperture 8 to the shape of the inner wall of the container1, and have been offset backwards so as to be flush. No part of theextruder 5 or of the screws 6 protrudes through the aperture 8 into thespace within the container 1.

The distance 18 here corresponds to about 5 to 10% of the radius 11 ofthe container 1 and to about half of the internal diameter d of thehousing 16. This embodiment therefore represents the second limitingcase or extreme value with the smallest possible offset or distance 18,where the direction 12 of rotation or of movement of the mixing and/orcomminution implements 3 is at least slightly opposite to the direction17 of conveying of the extruder 5, and specifically across the entirearea of the aperture 8.

The scalar product in FIG. 3 at that threshold point 20 situatedfurthest upstream is precisely zero, this being the point located at theedge that is associated with the aperture 8 and situated furthestupstream. The angle α between the direction vector 17 for the directionof conveying and the direction vector for the direction 19 of rotation,measured at point 20 in FIG. 3, is precisely 90°. If one proceedsfurther downwards along the aperture 8, i.e. in the direction 12 ofrotation, the angle between the direction vectors becomes ever greaterand becomes an oblique angle>90°, and at the same time the scalarproduct becomes negative. However, at no point, or in no region of theaperture 8, is the scalar product positive, or the angle smaller than90°. No local overfeed can therefore occur even in a subregion of theaperture 8, and no detrimental excessive stuffing effect can occur in aregion of the aperture 8.

This also represents a decisive difference in relation to a purelyradial arrangement, since there would be an angle α<90° at point 20 orat the edge 20′ in a fully radial arrangement of the extruder 5, andthose regions of the aperture 8 situated, in the drawing, above theradius 11 or upstream thereof or on the inflow side thereof would have apositive scalar product. It would thus be possible for locally meltedplastics product to accumulate in these regions.

FIG. 4 shows another alternative embodiment in which an extruder 5 withtwo co-rotating screws 6, one located vertically above the other, hasbeen displaced somewhat further than in FIG. 3 on the outflow side, butis still not tangential as in FIGS. 1 and 2. In the present case, asalso in FIG. 3, the rearward imaginary continuation of the longitudinalaxis 15 of the screws 6 passes through the space within the container 1in the manner of a secant. As a consequence of this, the aperture 8is—measured in the circumferential direction of the container 1—widerthan in the embodiment according to FIG. 3. The distance 18 is alsocorrespondingly greater than in FIG. 3, but somewhat smaller than theradius 11. The angle α measured at point 20 is about 150°, and thestuffing effect is therefore reduced in comparison with the apparatus ofFIG. 3; this is more advantageous for certain sensitive polymers. Theinner wall of the housing 16 or the right-hand-side inner edge, as seenfrom the container 1, is tangential to the container 1, and therefore,unlike in FIG. 3, there is no oblique transitional edge. At thisfurthest downstream point of the aperture 8, on the extreme left-handside in FIG. 4, the angle is about 180°.

1. An apparatus for the pretreatment and subsequent conveying,plastification or agglomeration of plastics, in particular ofthermoplastics waste for recycling purposes, with a container (1) forthe material to be processed, where the arrangement has, in thecontainer (1), at least one mixing and/or comminution implement (3)which rotates around an axis (10) of rotation and which is intended forthe mixing, heating and optionally comminution of the plastics material,where an aperture (8) through which the pretreated plastics material canbe removed from the interior of the container (1) is formed in a sidewall (9) of the container (1) in the region of the level of the, or ofthe lowest, mixing and/or comminution implement (3) that is closest tothe base, where at least one multiscrew conveyor (5) is provided toreceive the pretreated material, and has at least two screws (6) whichrotate in a housing (16) and which have conveying, in particularplastifying or agglomerating, action, where the housing (16) has,located at its end (7) or in its jacket wall, an intake aperture (80)for the material to be received by the screw (6), and there is aconnection between the intake aperture (80) and the aperture (8),wherein the imaginary continuation of the central longitudinal axis (15)of the conveyor (5) or of the screw (6) closest to the intake aperture(80), in a direction opposite to the direction (17) of conveying of theconveyor (5), passes, and does not intersect, the axis (10) of rotation,where, on the outflow side or in the direction (12) of rotation or ofmovement of the mixing and/or comminution implement (3), there is anoffset distance (18) between the longitudinal axis (15) of the conveyor(5) or of the screw (6) closest to the intake aperture (80), and theradius (11) that is associated with the container (1) and that isparallel to the longitudinal axis (15) and that proceeds outwards fromthe axis (10) of rotation of the mixing and/or comminution implement (3)in the direction (17) of conveying of the conveyor (5), and wherein thescrews (6) co-rotate.
 2. The apparatus according to claim 1, whereinthere are precisely two screws (6) provided or the conveyor (5) is aco-rotating twin-screw conveyor.
 3. The apparatus according to claim 1,wherein the screws (6) are cylindrical and are parallel to one anotheror the conveyor (5) is a parallel twin-screw conveyor.
 4. The apparatusaccording to claim 1, wherein the screws (6) are conical or the conveyor(5) is a conical twin-screw conveyor.
 5. The apparatus according toclaim 1, wherein one of the screws (6) is longer, preferably by a lengthgreater than or equal to 3 times the diameter (d) of the screw (6). 6.The apparatus according to claim 1, wherein, at least in the region ofthe intake aperture (80), the screws (6) intermesh tightly or touch. 7.The apparatus according to claim 1, wherein one of the cross sections ofthe screws (6) is vertically above the other, and the screws (6) in theimmediate region of the intake aperture (80) are in particularsymmetrical with respect to the centre of the intake aperture (80) andat an equal distance from the plane of the intake aperture (80).
 8. Theapparatus according to claim 1, wherein one of the cross sections of thescrews (6) is obliquely above the other or horizontally alongside theother, and only the screw (6) closest to the intake aperture (80) is inthe immediate region of the intake aperture (80).
 9. The apparatusaccording to claim 1, wherein the screws (6) or the screw (6) closest tothe intake aperture (80), viewed from the starting point that is closeto the intake or to the container, of the screws (6), or from the intakeaperture (80), in the direction towards the end or the dischargeaperture of the conveyor (5), rotate(s) clockwise.
 10. The apparatusaccording to claim 1, wherein, for a conveyor (5) in contact with thecontainer (1), the scalar product of the direction vector that isassociated with the direction (19) of rotation and that is tangential tothe circle described by the radially outermost point of the mixingand/or comminution implement (3) or that is tangential to the plasticsmaterial transported past the aperture (8) and that is normal to aradius (11) of the container (1), and that points in the direction (12)of rotation or of movement of the mixing and/or comminution implement(3) and of the direction vector (17) that is associated with thedirection of conveying of the conveyor (5) at each individual point orin the entire region of the aperture (8) or immediately radially infront of the aperture (8) is zero or negative.
 11. The apparatusaccording to claim 1, wherein the angle (α) included between thedirection vector that is associated with the direction (19) of rotationof the radially outermost point of the mixing and/or comminutionimplement (3) and the direction vector (17) that is associated with thedirection of conveying of the conveyor (5) is greater than or equal to90° and smaller than or equal to 180°, measured at the point ofintersection of the two direction vectors (17, 19) at the inflow-sideedge that is associated with the aperture (8) and that is situatedupstream in relation to the direction (12) of rotation or of movement ofthe mixing and/or comminution implement (3), in particular at the point(20) that is on the said edge or on the aperture (8) and is situatedfurthest upstream.
 12. The apparatus according to claim 1, wherein theangle (β) included between the direction vector (19) that is associatedwith the direction (12) of rotation or of movement and the directionvector (17) that is associated with the direction of conveying of theconveyor (5) is from 170° to 180°, measured at the point of intersectionof the two direction vectors (17, 19) in the middle of the aperture (8).13. The apparatus according to claim 1, wherein the distance (18) isgreater than or equal to half of the internal diameter of the housing(16) of the conveyor (5) or of the screw (6), and/or greater than orequal to 7%, preferably greater than or equal to 20%, of the radius ofthe container (1), or wherein the distance (18) is greater than or equalto the radius of the container (1).
 14. The apparatus according to claim1, wherein the imaginary continuation of the longitudinal axis (15) ofthe conveyor (5) in a direction opposite to the direction of conveyingis arranged in the manner of a secant in relation to the cross sectionof the container (1), and, at least in sections, passes through thespace within the container (1).
 15. The apparatus according to claim 1,wherein the conveyor (5) is attached tangentially to the container (1)or runs tangentially in relation to the cross section of the container(1), or wherein the longitudinal axis (15) of the conveyor (5) or of thescrew (6) or the longitudinal axis of the screw (6) closest to theintake aperture (80) runs tangentially with respect to the inner side ofthe side wall (9) of the container (1), or the inner wall of the housing(16) does so, or the envelope of the screw (6) does so, where it ispreferable that there is a drive connected to the end (7) of the screw(6), and that the screw provides conveying, at its opposite end, to adischarge aperture which is in particular an extruder head and which isarranged at the end of the housing (16).
 16. The apparatus according toclaim 1, wherein there is immediate and direct connection between theaperture (8) and the intake aperture (80), without substantialseparation, in particular without transfer section or conveying screw.17. The apparatus according to claim 1, wherein the mixing and/orcomminution implement (3) comprises implements and/or blades (14) which,in the direction (12) of rotation or of movement, have a comminuting,cutting and heating effect on the plastics material, where theimplements and/or blades (14) are preferably arranged or formed on or ata rotatable implement carrier (13) which is in particular a carrier disc(13) and which is in particular arranged parallel to the basal surface(12).
 18. The apparatus according to claim 1, wherein the manner offormation, set-up, curvature and/or arrangement of the frontal regionsor frontal edges (22) that are associated with the mixing and/orcomminution implements (3) or with the blades (14), act on the plasticsmaterial and point in the direction (12) of rotation or of movement,differs when comparison is made with the regions that, in the direction(12) of rotation or of movement, are at the rear or behind.
 19. Theapparatus according to claim 1, wherein the container (1) is in essencecylindrical with circular cross section and with a level basal surface(2) and with, orientated vertically in relation thereto, a side wall (9)which has the shape of the jacket of a cylinder, and/or the axis (10) ofrotation of the mixing and/or comminution implements (3) coincides withthe central axis of the container (1), and/or the axis (12) of rotationor the central axis are orientated vertically and/or normally inrelation to the basal surface (2).
 20. The apparatus according to claim1, wherein the lowest implement carrier (13) or the lowest of the mixingand/or comminution implements (3) and/or the aperture (8) are arrangedclose to the base at a small distance from the basal surface (2), inparticular in the region of the lowest quarter of the height of thecontainer (1), preferably at a distance of from 10 mm to 400 mm from thebasal surface (2).